In fuel cell systems with an anode recirculation cycle that runs overstoichiometrically, an undesired enrichment of nitrogen and water vapor occurs due to their diffusion through the membrane-electrode-assembly (MEA). This causes an impairment of the power density. So far, this phenomenon was avoided by a time dependent purge strategy. During this process a lot of unconsumed hydrogen gets wasted. A more efficient purge strategy that reduces the waste and improves the system efficiency, which operates load dependently by means of the mass transfer coefficient, is introduced. A comparison of the system efficiency with and without the load-dependent-purge-strategy (LPS) is made and discussed in order to demonstrate the effectiveness of the new method. Static as well as dynamic system simulations were performed for this purpose. A notable improvement of the system efficiency of up to 10% with LPS was achieved. With LPS the purge power losses could be markedly reduced. This reformation also induces an improvement of the system efficiency, which brings us a considerable step forward towards a longer reach. Moreover, LPS is not restricted to a certain fuel cell system and thus affords a more flexible and versatile employment than its predecessor.
Study on Heat and Mass Transfer Performance of Cathode Membrane Humidifier in Fuel Cell System
